InsaneAuto86

iTrader: (60)

Looking to keep costs down and pick up a junkyard shortblock to pair with my .030" milled L92 heads/LS3 intake. I want to have the best matched cam but am concerned about PTVC.

Would an LQ4 with dished pistons or flycutting an LQ9 be the better option? I know the cam will be a major factor, but am looking at the best starting point.

Goal is street car with as much TQ down low as possible.

Vesper TA

iTrader: (38)

I have unmilled l92's on my lq9, and pat g speced my cam at 226/234. He told me I couldn't go that much larger on duration due to ptv. I think a 229 or 231 is the max, but valve events have to be right for the heads.
I believe the lq4 piston is going to be the same cause the area around the rings is the same height as the flat tops. Only the center of lq4 pistons are dished, so you would have the same ptv clearance. I'm no expert tho, just passing on what I've researched.

Red99TA

iTrader: (11)

I'm no expert either but I do know when you run into PTV clearance issues it's closer to the center of the piston (where some are dished) - not near the rings.

Vesper TA

iTrader: (38)

Ahh ok, so it's the exhaust valve that has ptv issues?

Red99TA

iTrader: (11)

I think we're confusing each other. I had to flycut for the intake valve (exhaust had a ton of clearance). I thought you were saying it's close to the edge of the piston which at first I thought it wasn't that close but looking back at mine it actually is...I thought a dished piston would give you the required clearance this close to the edge - is the LQ4 piston not dished that far over?

Vesper TA

iTrader: (38)

Looking at my old lq4 pistons in the garage your flycut is pretty close to the flat top part over the rings. It only dishes in the center, which is why I thought it would give the same ptv clearance on the intake valve as a flat top piston.

Vesper TA

iTrader: (38)

here is a pic of an lq4 piston I have lying around.

Vesper TA

iTrader: (38)

Either way it's going to be really close especially with milled l92 heads.

InsaneAuto86

iTrader: (60)

Seems like it. So the better option would be the LQ9 and flycut.

Billy1987

iTrader: (10)

I am running a stock 03 lq4 with ls3 heads milled 0.03"s and i am running a pat g spec'd cam. 226/234 and have no problem. One thing to think about is what gaskets you run. I am running stock ls3 mls gaskets.

Vesper TA

iTrader: (38)

You would be able to run a bigger cam with the flycut lq9 pistons, but with the right speced cam milled l92's on stock lq4 pistons is doable. Just won't have a huge duration cam.

Vesper TA

iTrader: (38)

Same here on gaskets.